The order in which to compile Invalid Objects in schemas is SYS, SYSTEM, APPS and then all others. APPS_DDL and APPS_ARRAY_DDL should exist in all schema's.
In case of an ORA-1555 error while running adcompsc.pls, restart the script.

The script can be run as followed :

cd $AD_TOP/sql
sqlplus @adcompsc.pls SCHEMA_NAME SCHEMA_PASSWORD %

SQL> @adcompsc.pls apps apps %

After the script completes, check for invalid objects again. If the number has decreased, but invalid objects still exist, run adcompsc.pls again.
Keep running adcompsc.pls until number of invalid objects stops decreasing.

If there are any objects still left INVALID, verify them by using the script 'aderrchk.sql' to record the remaining INVALID objects.
'Aderrchk.sql' uses the same syntax as 'adcompsc.pls'. This script is also supplied with the Applications.
Send the aderrchk.sql to a file using the spool command in sqlplus.

e.g. sqlplus apps/password @aderrchk.sql SCHEMA_NAME SCHEMA_PASSWORD %
For objects which will not compile, try the following :

select text from user_source
where name = 'OBJECTNAME'
and text like '%Header%';
This script will provide the script that creates the packages/recreates the packages.

SQL>@packageheader
SQL>@packagebody

If recreating the package does not make the package valid, analyze the user_errors table to determine the cause of the invalid package :